1. Field of the Invention
The present invention relates to an image generating apparatus and an image generating method, which are capable of removing an unnecessary noise portion from a multi-valued image to generate an image with a necessary edge portion left therein.
2. Description of the Related Art
Conventionally, when an image includes a noise portion other than an edge portion, in a case of extracting edge information from this image to perform image processing, the influence of the noise portion is inevitable. In the case of executing image matching processing through use of edge information on an image including a noise portion to a large degree, for example, there has been problems in that the matching processing requires a long time, the matching accuracy is not improved, and the like.
In order to solve such problems, smoothing processing is often performed using, for example, an averaging filter, a Gaussian filter or the like so as to delete the noise portion (cf. “Handbook of Image Analysis”, by Mikio Takagi and Hirohisa Shimoda, Tokyo University Press, 1991, p. 539-543). However, performing the smoothing processing can delete the noise portion, but makes the edge portion further blurred.
Therefore, “Handbook of Image Analysis” discloses a use of a median filter which replaces a luminance value by a center value of a periphery. With the use of the median filter, it is possible to effectively remove dotted noise without losing the clearness of the edge portion.
Further, as disclosed in “Edge Preserving Smoothing”, (by Makoto Nagao and Takashi Matsuyama, “Computer Graphics and Image Processing”, Vol. 9, No. 4, 1979, p. 394-407), in a case of dividing an image with square regions, replacing a luminance value by a mean value of luminance values of a region with the smallest dispersion thereof among eight regions in the periphery of a prescribed region can perform the smoothing processing without losing the clearness of the edge portion.
Moreover, Japanese Unexamined Patent Publication No 2006-014024 discloses a noise removing method in which the smoothing processing is executed using only a pixel in which a difference in luminance value is within a prescribed threshold. Also in Japanese Unexamined Patent Publication No 2006-014024, it is possible to perform the smoothing processing without losing the clearness of the edge portion.